This proposal will focus on the following three subjects: developmental changes in electrophysiological properties of pre- and postsynaptic cells during formation of a synaptic contact, requirements for functional synaptic transmission, and neurospecificity in vitro. ACh receptor accumulation to the cultured Xenopus neuromuscular contacts was clearly demonstrated by fluorescent staining of alpha-bungarotoxin binding sites. Changes in properties of miniature endplate potentials (mepps) associated with ACh receptor accumulation will be studied. Electrophysiological properties of presynaptic neurons will be examined during development in culture. Requirements for synaptic transmission will be determined in neuromuscular contacts between two neuronal cell lines and a rat skeletal muscle cell line. Use of clonal cell lines for analysis of synaptic interaction is a unique approach and will facilitate biochemical characterization of presynaptic neuronal properties. Some expression of neurospecificity--i.e., competition between two presynaptic neurons or between two postsynaptic cells, will be examined in culture. Combination of electrophysiological, morphological and cell culture techniques will elucidate mechanisms occurring in early synaptic interaction between nerve and muscle.